Satellite Laser Ranging & Tracking

When the Space Geodesy Facility at Herstmonceux, East Sussex
faced reliability problems with their ageing telescope, their engineers turned
to Heason Technology for expert assistance.

The thirty year old telescope forms part of
a global tracking network to monitor the paths of Earth-orbiting
satellites to quantify, for example, the amount by which sea level is currently
rising. The scientists at Herstmonceux track passing orbital
satellites and accurately calculate their distance (to an accuracy of 1mm)
by firing a high-powered pulsed laser against a satellite-mounted reflector and
measuring the return time delay. With orbiting satellites at passing range of
between 400 and 20,000 kilometres, tracking accuracy is extremely
important (to within +/- 1 arc seconds).

Heason were first commissioned to evaluate the existing telescope
set-up. Their conclusion verified the users own thoughts that the actual
telescope motion hardware had effortlessly stood the test of time, but the
antiquated electronics were considerably more suspect. Furthermore, technical
support on the drive package was more or less non-existent from the original
manufacturer.

Heason successfully tendered for the upgrade programme,
which included replacing all of the existing analogue control system with an
up-to-date digital package. Heason selected a Delta Tau PMAC motion controller
to form the heart of the system. The PMAC ultralite model was
specified to be located within the host PC (which generates the predicted
satellite path) with Delta Tau’s MACRO network connecting to the drive and
feedback interfaces located remotely in a new motion control cabinet. Heason
provided new linear power amplifiers, along with new inductosyn and resolver
interfaces complete with a revamped I/O and logic control strategy.

Working closely with the Herstmonceux technical experts,
Heason’s software engineers developed a motion control application code to
interface to the host computer taking new motion control demand data from the
customers host at 10Hz (with the ability to operate up to 1KHz) and controlling
the telescope motion to accurately track passing satellites to with +/- 1
arc-seconds.